In code division multiple access (CDMA) communication systems, such as the well known system based on the IS-95 standard, a pilot signal, considered a pilot channel, transmitted from a base station contains data that are known by all mobile stations compatible with the system. Each mobile station communicating with the base station receives the pilot signal to extract important information about phase rotation, channel gain estimation, signal-to-noise plus interference ratio estimation, and others. Such important information collectively or individually are referred to as the channel estimate. A mobile station decodes a data signal considered a data channel, also transmitted from the base station to the mobile station uses the channel estimate to perform coherent demodulation of the data channel symbols. The transmitted signal carries information data such as voice. The mobile station performance of decoding the data symbols directly depends on the accuracy of the channel estimate.
In another well-known system based on the Wideband CDMA (WCDMA) standard, the pilot signal is embedded with the data signal. Therefore, each signal, considered a communication channel, transmitted from a base station to a mobile station contains pilot and data symbols. The terms: bits and symbols are used interchangeably. A mobile station receives a burst of symbols that contains the pilot and data, and other controlling data information. The burst of data containing the pilot and data symbols spread over a wide frequency spectrum according to a predefined code sequence known to all mobile stations compatible with the system. All mobile stations compatible with the system also know the content of the pilot data. A mobile station receiving a burst of data decodes the pilot data bits by knowing the spreading code and processes the pilot data symbols to determine the channel estimate. The channel estimate is used for coherently demodulating the data symbols. One ordinary skilled in the art may appreciate that the number of pilot data symbols in the transmitted signal directly effects the accuracy of the channel estimation, however, the data burst is of a limited duration and its time limit can not be used to transmit large number of pilot symbols in comparison with the number of data symbols in the same burst in order to improve the accuracy of the channel estimate. The pilot data symbols are considered overhead data and affect the throughput efficiency of the communication system. The communication system operating based on the IS-95 standard may not have such a problem because the pilot signal is transmitted separately at a relatively high power level and the mobile station may decode as many pilot data bits as it may require to assure an adequate and accurate channel estimate.
Therefore, there is a need for a method and apparatus for decoding data information based on accurate channel estimation derived from a limited number of pilot data bits in a data burst in a WCDMA communication system.